As semiconductor integrated circuits have become finer and more highly integrated, the steps of semiconductor manufacturing processes have become more numerous and complex. Consequently, the surfaces of semiconductor devices are not always flat. The presence of steps in the surfaces of semiconductor devices leads to step breakage in wiring, and local increases in resistance and may cause wire breakage and a drop in electrical capacity. Furthermore, in the insulating films, this may lead to a deterioration in the withstand voltage and the occurrence of leakage, etc.
Meanwhile, as semiconductor integrated circuits have become finer and more highly integrated, the light source wavelengths of semiconductor exposure apparatuses used in photolithography have become shorter, and the numerical aperture or so-called NA of the projection lenses of semiconductor exposure apparatuses has become larger. As a result, the focal depths of the projection lenses of semiconductor exposure apparatuses have become substantially shallower. In order to handle such shallow focal depths, there has been a need for a greater degree of flattening of the surfaces of semiconductor devices than in the past.
One of the methods known in the art for polishing process wafers, which are, for example, wafers that have semiconductor circuits formed inside, is CMP (chemical mechanical polishing or planarization). CMP is particularly efficient technique for flattening large areas (at the die size level). CMP is a process in which the surface layer of a process wafer is removed by the combined action of a chemical effect and physical polishing, and is an important technique for global flattening and electrode formation. The process uses a polishing agent called a slurry. The slurry is formed by dispersing polishing particles (generally silica, alumina or cerium oxide, etc.) in a solubilizing solvent such as an acidic or alkaline. In CMP, polishing is caused by pressing the surface of the wafer with the polishing pad of the polishing tool, which has a polishing pad, thus causing friction by the relative motion.
Unlike a wafer in a blank state, the surface of a patterned wafer is not flat. In particular, there are ordinarily steps between portions where chips are formed and portions where chips are not formed. Accordingly, in cases where such patterned wafers are polished, it is necessary to eliminate local indentations and projections (this is called “local pattern flatness”) while performing uniform polishing (this is called “global removal uniformity”) in accordance with large-period indentations and projections (undulations) in the wafer substrate, i.e., along such indentations and projections (undulations).
Conventionally, in order to meet such requirements, a so-called two-layer pad in which a hard polishing pad and a soft pad are bonded together has been used as a polishing body in the polishing tool, and this two-layer pad is bonded to the surface of a polishing platen which contains a rigid body so that the hard polishing pad is located on the side of the object of polishing. An IC1000 (commercial name) manufactured by Rodel, Inc. has been used as the hard polishing pad; grooves used for the supply and discharge of the polishing agent are formed in the surface of this pad. In the case of this hard polishing pad, the thickness of areas in which no grooves are formed is 1.27 mm, the depth of the grooves is approximately 0.6 mm, and the residual thickness in areas where grooves are formed is approximately 0.67 (=1.27−0.6) mm. Furthermore, sponge-form Suba400 (commercial name) manufactured by Rodel, Inc. has been used as the soft pad.
If a polishing body consisting of such a two-layer pad is used, since a soft pad is interposed between the hard polishing pad and the polishing platen, the soft pad is relatively susceptible to compressive deformation. Accordingly, the hard polishing pad undergoes deformation in accordance with the large undulations of the patterned wafer. Consequently, polishing can be performed with a fixed amount of polishing along the undulations of the patterned wafer. On the other hand, since the hard polishing pad is relatively resistant to deformation with respect to local indentations and projections, local indentations and projections can be removed by polishing.
However, there is now a requirement to increase the degree of integration of semiconductor integrated circuits to a point beyond that seen in the past, and to apply a finer wiring rule. Furthermore, there has been an increase in the demand for polishing system LSI, and the pattern density distribution of system LSI has become more severe.
Thus, in cases where patterned wafers that have patterns determined by a fine wiring rule or patterns with a severe density distribution formed inside are polished, even if conventional polishing bodies such as those described above are used, it is difficult to satisfy the requirements of both “global removal uniformity” and “local pattern flatness.” Specifically, in these wafers, local indentations and projections tend to be large, and in cases where a conventional polishing body, such as that described above, is used the soft pad tends to undergo compressive deformation as the local indentations and projections increase, and the hard pad also undergoes deformation in accordance with this. As a result, the ability to eliminate steps is reduced, so that it becomes difficult to ensure “local pattern flatness.”
Accordingly, the present invention relates to a polishing body that contains in order a polishing pad that has grooves formed in the surface, a hard elastic member and a soft member. For example, the hard elastic member is an elastic member with a Young's modulus of 10,000 kg/mm or greater. The soft member is a member with a compression rate of 10% or greater when pressed with a pressure of 1.0 kg/cm2.
If this polishing body is used, since a hard elastic member is sandwiched between the polishing pad and the soft member, the ability to eliminate steps can be increased, thus improving the “local pattern flatness,” while ensuring “global removal uniformity.”
It is desirable that a hard pad be used as the polishing surface-side polishing pad that is employed in this polishing body. Accordingly, it is conceivable that an IC1000 (commercial name) manufactured by Rodel, Inc., in which the thickness of areas in which no grooves are formed is 1.27 mm, the depth of the grooves is approximately 0.6 mm, and the residual thickness of the areas in which grooves are formed is approximately 0.67 (=1.27−0.6) mm, might be used “as is” as the polishing pad on the polishing surface side of this polishing body in the same manner the hard pad of the conventional polishing body described above.
However, in a polishing body in which a hard elastic member is included, in spite of the fact that the polishing pad on the polishing surface side has an inherently long useful life in terms of the ability to eliminate steps, this polishing pad is subject to restrictions arising from the depth of the grooves in this polishing pad, so that the useful life of this polishing pad is shortened.
Specifically, the thickness of the polishing pad on the polishing surface side of the polishing body becomes smaller as a result of wear caused by polishing of the object of polishing and wear caused by dressing. Dressing is a treatment that eliminates clogging of the polishing surface, and is also called conditioning). Meanwhile, the grooves in the surface of the polishing pad are indispensable for the supply and discharge of the polishing agent during polishing, and if these grooves are eliminated or reduced to a specified depth or less, it becomes impossible to obtain the desired polishing characteristics. Accordingly, in cases where the IC1000, which has the thickness and groove depth described above, is used even if it is assumed that the useful life is not exhausted to the point where the grooves are eliminated, the useful life is exhausted at the point in time at which the thickness of areas in which no grooves are formed is reduced to a value of 0.67 (=1.27−0.6) mm. The polishing pad is no longer useful because of the restrictions arising from the fact that the grooves are indispensable. However, it has been ascertained that when a polishing body includes a hard elastic member, even if the thickness of the polishing pad on the side of the polishing surface is less that 0.67 (=1.27−0.6) mm, the ability of the polishing body to eliminate steps is actually slightly improved rather than diminished.
Thus, in a polishing body in which a hard elastic member is not included, if a conventional polishing pad is used “as is,” the pad is subject to the restrictions of groove depth, so that the useful life is needlessly shortened.
Furthermore, a polishing body consisting of the two-layer pad described above is not as desirable as the polishing body that includes a hard elastic member. First, the two-layer pad's ability to eliminate steps is inferior to that of the polishing body with an interposed hard elastic member. Second, the ability of the two-layer pad to eliminate steps is further reduced as the thickness of areas in which no grooves are formed in the polishing pad on the polishing surface side becomes smaller. Therefore, even if an IC1000 with the thickness and groove depth described above is used, the pad is subject to restrictions from the standpoint of the ability to eliminate steps, so that the useful life is exhausted before the grooves disappear. Accordingly, in the case where a polishing body consists of a two-layer pad, the useful life cannot be extended at all even if the grooves in the polishing pad on the side of the polishing surface are made deeper.